Galvanometer suspension



Dec. 6, 1960 J. L. FISHER GALVANOMETER SUSPENSION Filed Feb. 2e, 1959 Y f fG.

INV ENT OR.

4 FIGS United States Patent() GALVAN OMETER SUSPENSION .lames L. Fisher, Tulsa, Okla., assignor to Century Geo- Filed Feb. 26, 1959, Ser. No. 795,763

7 Claims. (Cl. 324-97) This invention relates to galvanometers of the type wherein a coil of tine wire and an indicating device such as a mirror are suspended by ribbons between fixed supports, the assembly being disposed in a magnetic held, as from one or more permanent magnets. In particular, the present invention is directed to a galvanometer assembly characterized by greatly improved means for damping or inhibiting unwanted transverse or longitudinal vibratory movement of the sensitive assembly comprising the coil, mirror, and suspension ribbons.

In the presentinvention, such damping means comprise a plurality of open-ended capillary tubes surrounding the suspension ribbons at strategic locations therealong, the capillary tubes being permanently filled with a viscous liquid of suitable characteristics.

Thus, a major object of the present invention is to provide, in a galvanometer assembly, an improved means for damping unwanted movements of the sensitive assembly which would otherwise occur as the result of shock, vibration, or' acceleration.

In furtherance of the aforementioned major object, a further object of the present invention is to provide a galvanometer assembly in which capillary tubes are disposed around selected parts of the ribbon assembly at locations effective to damp out transverse or longitudinal movement thereof, such capillary tubes being open-ended and filled with viscous liquid effective to inhibit undesired movement of the assembly without significantly affecting the desired rotatory movement of the assembly in response to magnetic forces.

Still another object of the invention is to provide, in a galvanometer assembly, capillary damping tubes of a novel type into which the suspension ribbon of the galvanometer assembly can readily be inserted during assembly and which can be readily filled with liquid either before or after the basic parts of the galvanometer have been assembled.

A still further object of the invention is to provide a galvanometer assembly wherein capillary tubes filled with viscous liquid are disposed around the suspension ribbons at strategic positions therealong, and wherein the portions of the ribbon above and below the respective capillary tubes are provided with beads having non-Wetting characteristics effective to prevent the fluid from the capillary tubes from creeping along the suspension ribbon and hence escaping from the capillary zone and onto the coil assembly, mirror, or other galvanometer components.

Other objects and advantages of the invention will appear from the following detailed description of a typical embodiment thereof.

ln the appended drawing, Figure l is a longitudinal sectional View of a typical galvanometer element ernbodying the principles of the present invention, shown in the environment wherein it is customarily used, that is, mounted between a pair of pole pieces adapted to provide a fixed magnetic field around the galvanometer coil. Fig.

ICC

2 is a view. in side elevation, of the basic galvanometer assembly of the Fig. 1 embodiment, shown with its outer protective jacket removed and shown in a position rotated ninety degrees with respect to the Fig. l showing. Fig. 3 is a side elevation view of the ribbon suspension proper of the Fig. l galvanometer, showing in somewhat larger scale the coil, the mirror, and the suspending ribbons which hold it between fixed supports. Fig. 4 is a transverse sectional view along the line 4-4 of Fig. 2, which brings out the structural detail of the fret which bears against the ribbon near its upper end and defines the upper limit of the rotatory motion. Fig. 5 is a transverse sectional view along the line 5-5 of Fig. 2, showing in detail one of the capillary damping tubes which is used in the present invention and showing the manner in which it is carried within the internal frame of the apparatus. Fig. 6 is a transverse sectional view along the line 6 6 of Fig. 2, showing the detail of the intermediate capillaryA tube which surrounds the suspension ribbon between the mirror and the coil. Fig. 7 is a transverse sectional View along the line 7-7 of Fig. 2,y showing how the coil may be supported in its middle portion by a spacer. Fig. 8 is a transverse sectional view along the line 8-8 of Fig. 2, showing the lower capillary tube and the manner of its suspension within the internal v frame of the structure. Fig. 9 is a greatly enlarged fragmentary View of a portion of the suspension ribbon, showing one of the beads which prevent the capillary liquid from creeping along the ribbon. Fig. l0 is a transverse sectional View along the line lll-l0 of Fig. 9, showing in further detail the structural relationship of the suspension ribbon and the bead. Fig. ll is a perspective view of a typical capillary tube of the type used in my invention for damping.

As may be observed from Fig. l, my galvanometer will normally be mounted in a cylindrical rigid outer housing 20 made of non-magnetic metal such as beryllium copper or other suitable material. The outer housing 20 functions primarily to provide mechanical strength for the galvanometer assembly. The apparatus cornprising the sensitive components of the galvanometer are mounted on an internal frame 21 disposed coaxially within the outer housing 20. A sleeve 22 made of insulating material separates the internal frame 21 from the housing 20. Internal frame 21 may be made of brass or other nonmagnetic metal.

Near the middle of housing 20, a relieved zone 23 is provided into which a transparent window 24 is cemented or otherwise suitably secured. As persons skilled in the art will understand, window 24 serves the purpose of permitting light from an outside source to impinge on the galvanometer mirror and be reflected therefrom onto a photosensitive film or the like.

Slightly below the location of window 24, the outer diameter of housing 21 is reduced so as to define a step or shoulder 25, the diameter of housing 20 being uniform below the shoulder 25, to permit its being inserted between a pair of magnetic pole pieces 26 and 27, the adjacent faces of the pole pieces being suitably recessed to accommodate the housing 20. At its bottom end, the internal frame 2l projects below the lower extremity of the housing 20 and terminates in a conventional plug 28, comprising a pair of electrical contact rings 29 and 30 separated by an insulating sleeve 3i'. The upper contact ring 3l) is electrically connected to the internal frame 21, while the lower contact ring 29 is connected through internal conducting means (not shown) to the bottom ribbon support 32. An internal insulator within the plug 28 provides electrical isolation between the ribbon support 32 and the frame 21. Since the plug 28 and its electrical characteristics are conventional in Y 3 th galvanometer art', itis believed that detailed disclosure of its structure is unnecessary.

A closure plug 33 is threadedly disposed in the top portion of- -the housing 20, as shown in Fig. l.

I shall now describe inY some detail the structur of the sensitive parts of the galvanometer apparatus carried on internal frame 21. 4

l VAs may be observed from Figs. 1 and 2the internal frame 21 is generally-cylindrical in shape, but its walls are relieved in various zones along its length to provide Vconvenient access to the various components mounted on the' frame. At the upper end of frame 21, itis formed to dene an Vupper support or anchoring member 34, from which a ltension spring 35 depends.. To the lower end of spring 35, then upper suspension ribbon 36 is secured. Upper suspension ribbon 36,y the corresponding lower suspension ribbon 31',V and theintermediate suspension ribbon38 are customarily made of gold, although other electrically conducting materials of suitable physical lproperties may be employed for that purpose. l i

The suspension ribbon 36 posses downward from the spring 35, over the fret 39, and through the upper capillary tube 40, being joined at its -lower end to the mirror 41.Y

The lower end of the galvanometer mirror 41v isrconneoted to the upper end of coil 42 by means of intermediate suspension ribbon 3S, ribbon 38 passing, between the mirror and the coil, through the intermediate capillary tube 43. Y Y

The coil 42 is wound of-very tine wire in the usual elongated shape, spools 44 and spacer 45 being provided to hold the coil in the desired shape.

The lower end-of the coil 42 is joined to lower suspension ribbon 37, which passes through lower capillary tube 46 and terminates on the bottom support member 32 already mentioned. Y

It will be understood, in accordance with conventional practice, that the mechanical suspension between the coil 42 and the rib-bons 37 and 38 is made via the spools 44, and the respective terminal-s of the wire coil 42 arel connected to the ribbons 37 and 38, so that the ribbons provide a convenient means for passing electrical current from an external source through the coi1-42; In that connection it should be noted that the mirror 41l is carried within anelectrically Vconducting support which is joined to the suspension ribbons 36 and 38, providing an elect'rically continuous path `from ribbon 38 to ribbon 36 and hencevthrough spring 35 to the frame 21.

From the foregoing description, it will beunderstood that an external electrical circuit connected to the contact rings 29 and 3h wili be completed'through the coil 42 via the frame 21 and the various suspension means above mentioned.

The fret 39 may be made of brass or like material and mayI be silver-soldered or otherwise' rigidly secured to the frame 2l.

surfaces and thus be lost, the top and bottom surfaces '43a and the facing edges 4317 (Fig. ll) of Yeach capillary Y tube are coated with a thinlayer of a material such as Teilon plastic which resists wetting by the capillary liquid.

Above and below each of the capillary tubes, the ribbon which passes therethrough is provided with a bead 48 completely surrounding the ribbon. The beads 48, the structure of which may be most plainly noted in Figs. 9 and l0, are made of a material such as Teflon plastic which resists ywetting by the liquid carried in the capillary tubes. This liquid is preferably an oil whose viscosity is relatively -independent of temperature. The silicone oil sold under tbc trade name Dow Corning No. 200 has been found satisfactory for -thfs purpose.

The beads 48 prevent the liquid in the capillary tubes from creeping along the suspension ribbons, and they form an important part of the present invention.

The length of the various capillary tubes andthe viscosity of the liquid carried therein may be varied considerably as a matter of design, depending on the structural characteristics of the assembly as a whole and the resulting requirements for effective damping of the suspended assembly against transverse and longitudinal movement. Specifically, I have foundrthat, for most applications, the upper and lower capillary tubes may be approximately equal in length and may beV filled with o il having viscosity 0f the order cfa few thousand centi- Stokes, The intermediate capillary vtube 43, however, should normally be shorterthan the other capillary tubes andyshould preferably be filled with an oil having much higher viscosity than that which is used in the upper and lower tubes. g l Y Y Y In one typical embodiment of my invention, kthe upper capillary tube 40 was 0.14 inch in length, had an internal diameter of .016 inch, and was filled with an Voil having a viscosity of 12,500 centistokes. YIn the same embodiment, the bottom capillary tube was 0.1 inch in length, hady an internal diameter of .016 inch, and was filled with an oil having a viscosity of 6,000 centistokes. The intermediate capillary tube in that same embodiment had Y a length of 0.04.7y inch, had an internal diameter of .014

inch, and was filled with an oil having a viscosityof 200,000 centistokes. Y

In thetypical embodiment just discussed, the coil and mirror together had a total mass of 4.65 milligrams and a total torsional moment of inertia of 6.59)(10-6 gram cm?. v

In galvanometers of dilerent mass and torsional inertia properties, the size of the capillary tubes and Vthe viscosity of the oil carried therein will of course be adjusted appropriately to achieve proper damping.

Preferably, the tension spring 35 should be submerged in a matrix ofY grease, which tends to damp out vibra- The capillary tubes 46, 43,' and 46 may also be made of Y brass or similar material and likewise may be silversoldered or otherwise rigidly secured to the frameV 21. As may be seen from Figs. 5, 6, 8, and ll, the4 capillary tubes are so formed as to dene a small central aperture axially'disposed within the tube, theraperture being of diverging in its outer zone, as is shown' clearly in Figs. 5,

6, and 8. The width of the slot in the various capillary tubes-is suiliciently small in the portion adjoining the central aperture so as to enable capillary'forces of the liquid in the centralv aperture to hold the liquid within'` Y the tube despite the presence of the slot. Toinsure that liquidin the'capillary tubes willnot iiow out over the tube tion. I have found Dow Corning stop cock grease to be satisfactory for this purpose. y Y

The intermediate capillary tube, with its high-viscosity liquid, ysupplies most of the torsional damping and should therefore be located near the center of the moment of inertia of the assembly. In galvanometers wherein the coil is tied tightly in its mid-section, as disclosed in Hendricks Patent No. 2,622,118, the intermediate capillary tube may be disposed so as to surround the, coil in its tied zone. v When this is done, the inner diameter of the capillary tube must of course be chosen so as to accommodate the coil. The larger internal diameter of the intermediate capillary tube thus made necessary does not present a practical problem from the standpoint of liquid escape, however, since the high-viscosity oil normally used in the intermediate capillary tube will readily hold its position within the tube notwithstanding the greater size ofthe central opening. y

In .the assembly of my kgalvanometer, the parts can all be mounted on the Yframe 21, the relieved zonesY in the wallV of frame 21 providing convenient accessl for 'Y purposes'of'assembly. In the assembly operation, the

side slots in the Various capillary tubes greatly facilitate the introduction therein of the suspension ribbons.

When the assembly of the parts on the frame 21 has been completed, the damping liquid may be introduced into the capillary tubes by means of hypodermic syringes equipped with needles of appropriate size. When the forming and balancing of the assembly have been completed, the frame 21 may be slid into the outer housing 20 with the insulator sleeve 22 in position.

Galvanometers made according to my invention enjoy the advantage, as compared to prior-art galvanometers, that the capillary damping tubes do not upset the static balance of the coil-mirror assembly. This feature of my invention permits the various sensitive parts of the galvanometer to be statically balanced at the time of initial assembly, with the assurance that they will not prove to be unbalanced when the galvanometer has been completed and is ready for use.

In the foregoing specification, I have described the filamentary suspension means used in my galvanometer as being a ribbon, preferably made of gold or a suitable alloy thereof. It will be understood by readers skilled in the art that various types of suspending filaments other than gold ribbons may be, and commonly are, used in sensitive galvanometers. In some instances, the suspension means in a sensitive galvanometer may be a thin iilament of substantially circular or oval cross section.

Hence, in the claims appended hereto, the term lamentary suspension means and similar language is used to refer broadly to the entire class of suspension filaments used in sensitive galvanometers, specifically including ribbons, wires, and threads.

While I have in this specification described in considerable detail a typical embodiment of my invention, it should be understood that many departures from the specitic structure disclosed in the drawing may be made by skilled readers without departing from the spirit of my invention. It is accordingly my desire that the scope of the invention be determined primarily by reference to the appended claims.

I claim:

l. In a glavanometer assembly of the type comprising a coil, a mirror, a pair of relatively fixed spaced supports, iilamentary suspension means joining said mirror and coil, and other iilamentary suspension means suspending said coil and mirror between said supports, the improvement which comprises an open-ended capillary tube containing liquid held therein by capillary forces, said tube being substantially shorter than said coil and being disposed around said first-mentioned suspension means between said mirror and said coil, a part of said rst-mentioned suspension means being immersed in said liquid, said first-mentioned suspension means having iixedly disposed thereon, flanking the portion thereof immersed in said liquid, a pair of sho-rt beads formed of material substantially unwettable by said liquid, operative to prevent creeping of said liquid therebeyond.

2. In a galvanometer assembly of the type comprising a coil, a mirror, a pair of relatively fixed spaced supports, and iilamentary suspension means suspending the coil and mirror between said supports, the improvement comprising at least one open-ended capillary tube containing liquid held therein by capillary forces, said tube being disposed around a part of said assembly, such part being immersed in the liquid in said tube, said assembly having tixedly disposed thereon, flanking the part thereof immersed in said liquid, a pair of short beads formed of material substantially unwettable by said liquid, operative to prevent creeping of said liquid past said barrier means.

3. In a galvanometer assembly of the type comprising a coil, a mirror, a pair of relatively iXed spaced supports, and iilamentary suspension means suspending the coil and mirror between said supports, the improvement comprising a plurality of open-ended capillary tubes including a iirst tube situated relatively near one yof said supports, a second tube situated relatively near the other of said supports, and a third tube situated closer to the center of the moment of inertia of said assembly than to either of said supports, all three of said tubes containing liquid held therein by capillary forces and all of said tubes being disposed around said assembly whereby discrete portions of said assembly are respectively immersed within the liquid respectively carried in said three tubes.

4. in a galvanometer assembly of the type comprising a coil, a mirror, a pair of relatively iixed spaced supports, and filamentary suspension means suspending the coil and mirror between said supports, the improvement comprising a plurality of open-ended capillary tubes including a first tube situated relatively near one of said supports, a. second tube situated relatively near the other of said supports, and a third tube situated closer to the center of the moment of inertia of said assembly than to either of said supports, all three of said tubes containing liquid held therein b-y capillary forces and all of said tubes being disposed around said assembly whereby discrete portions of said assembly are respectively immersed within the liquid respectively carried in said three tubes, the Viscosity of the liquid in said third tube being much greater than the viscosity of the liquid in either of said other tubes.

5. In a galvanometer assembly of the type comprising a coil, a mirror, a pair of relatively fixed spaced supports, and filamentary suspension means suspending the coil and mirror between said supports, the improvement comprising a plurality of open-ended capillary tubes including a iirst tube situated relatively near one of said supports, a second tube situated relatively near the other of said supports, and a third tube situated closer to the center of the moment of inertia of said assembly than to either of said supports, all three of said tubes containing liquid held therein by capillary forces and all of said tubes being disposed around said assembly whereby discrete portions of said assembly are respectively immersed within the liquid respectively carried in said three tubes, the portions of said assembly respectively adjacent said three tubes having fixedly disposed thereon short beads formed of material substantially unwettable by the liquid in said respective tubes, said beads being disposed in pairs flanking the ends `of said tubes and being operative to prevent creeping of liquid from said tubes past said respective barrier means.

6. Apparatus as defined in claim 5 wherein the liquid in said third tube has viscosity very much greater than the liquid in either of said other tubes.

7. In a galvanometer assembly of the type comprising a coil, a mirror, a pair of relatively iixed spaced supports, and filamentary suspension means suspending the coil and mirror between said supports, the improvement comprising at least one open-ended capillary tube containing liquid held therein by capillary forces, said tube being disposed around a part of said assembly, such part being immersed in the liquid in said tube, said assembly having fixedly disposed thereon, anking the part thereof immersed in said liquid, a pair of short beads formed of material substantially unwettable by said liquid, operative to prevent creeping of said liquid past said barrier means, and said capillary tube being coated on its surfaces adjacent said liquid with a thin layer of material substantially unwettable by said liquid, operative to prevent ow thereof over said coated surfaces.

References Cited in the tile of this patent UNITED STATES PATENTS 1,951,578 Peters Mar. 20, 1934 2,596,019 Fisher May 6, 1952 2,719,264 Murray Sept. 27, 1955 2,882,498 Turre Apr. 14, 1959 

